BuddyPress.org

I have an issue with new user activation link. I have WP 3.2.1 Sub-domains Multisite and BP 1.5.
BP is running on a sub-domain, and there are 5 other sub-domains.

When a new user registers on primary site, he receives activation email and the link is pointing to BP blog,
I believe it should be “http://domain.com/wp-activate.php?key=xxx” but it is “http://sub-domain.domain.com/wp-activate.php?key=xxxx”

where sub-domain is buddypress site.

Please suggest how to correct this, activation link should point to main domain only.